The invention relates to an apparatus for the winding of helical springs with a rotationally driven winding mandrel, provided with a radial slot at its forward end for the reception of the spring wire, which can be axially dispaced from a withdrawn initial position towards a projecting final position.
In known apparatus of this type--such as described, for example, in U.S. Pat. No. 952,582 and in German Patent No. 585,792--the end of the spring wire is positioned in the radial slot at the forward end of the winding mandrel and, therethrough, clamped to the winding mandrel. The winding mandrel is then powered into rotation and draws the spring wire from the supply coil and winds it spirally on itself. Corresponding to the increased length of the wound wire, or of the spring into which it was wound, the winding mandrel is slid axially out from the machine housing which contains the mandrel drive.
As soon as the mandrel has reached its end position, upon being pushed out to its full extent, the forward end of the wire will be pushed out of the radial slit of the mandrel with the increasing length of the helical spring. The spring is, thereupon, no longer entrained by the rotational movement of the mandrel and the spring winding process is interrupted. Consequently, winding machines of the prior art can only wind springs whose length does not exceed the length of the winding mandrel. Since the length of the winding mandrel is limited by consideration of mechanical stability, the length of the helical springs which may be wound on the known winding machines on a mandrel is also limited.
It is a principle object of the invention, therefore, to provide apparatus for the winding of helical springs, wherein the length of the spring which may be wound thereon is not limited by the length of the mandrel, so that helical springs of any desired length may be wound.
This and other objects are attained by a device of the type described in the introductory paragraph, through the provision of a transfer head adjacent to the final position of the mandrel, with a guide channel passing through the transfer head in coaxial alignment with the mandrel, for the passage of the wound spring therethrough, and wherein at least one roller, radially pressed against the forward end of the mandrel when it is in its final position, is provided on the transfer head, and wherein the transfer head is rotationally driven together with the mandrel, and synchronously therewith.
The apparatus of the invention permits the windings of helical springs of any desired length in the following manner.
Initially, as with a spring winding machine of the prior art, the end of the spring wire is located in the radial slot at the forward end of the mandrel. The mandrel is set into motion and draws the spring wire and winds it into a helical spring. The mandrel slides forward with the increasing length of this wound spring, until it had been axially displaced for its full length, into its final position.
Before the mandrel reaches its final position, the forward end of the mandrel slides into the transfer head. The one, or more, rollers on the transfer head are pressed, under load, onto the outer surface of the helically wound spring and press it, in turn, radially against the forward mandrel end portion. As the beginning of the spring wire is pushed from the radial slot of the winding mandrel, upon the continuation of the winding process, the helical spring continues to be entrained by the rotating mandrel since the rollers lock the spring radially inward against the mandrel.
Since the rollers are, themselves, rotationally free, and since the entire transfer head is rotated in synchronism with the winding mandrel, the rollers lock the helical spring against the mandrel but do not impede the forward displacement of the spring axially along the mandrel. The spring may, therefore, be further wound into any desired length; with the wound spring exiting through the guide channel of the transfer head.
So as to ensure that the rollers can press the helical spring against the mandrel with a high load, and yet not impede the axial forward travel of the spiral spring with respect to the mandrel, it is important that the spring should be able to set the rollers into rotational motion despite the high compression load. For this purpose it is advantageous to provide teeth on the periphery of the rollers, with the spacing of the teeth corresponding to the lead of the spring coils. The teeth, therefore, enter always between the individual spring coils, so that the rollers can be easily rotated even with a negligible axial forward pressure of the wound spring.
Furthermore, the unhindered forward movement of the helical spring is favored, despite the high compression loads of the rollers, by a conical development of the mandrel.
Even a small taper of the mandrel results in a material improvement of the ease of forward translation of the helical spring.
The entrainment of the wound helical spring on the rotating mandrel is further assisted by the inherent tendency of the helical spring to lock itself automatically under a torsional load against the mandrel. Initially the spring is only held by its forward end against the mandrel by the rollers and rotated along with the mandrel. At the rearward end of the mandrel, where the spring wire is led onto the mandrel an opposing tension is imposed on the wire, since the wire must be pulled off the supply coil by the rotation of the mandrel. In this manner, the helical spring is placed under a torsional load over its entire length along the mandrel. This torsion results in a reduction in the cross-sectional diameter of the helical spring and, consequently, in a locking of the spring against the tapered outer surface of the mandrel along its entire length. This self-induced locking of the spring on the full length of the mandrel makes possible the transfer of the entire torque of the winding mandrel onto the wire being drawn from its supply coil with a relatively negligible clamping load exerted by the rollers of the transfer head.
The apparatus of the invention permits the manufacture of helical coil springs of any desired length. Therefore, the length of the spring which may be made is no longer restricted by the length of the winding mandrel. The apparatus of the invention may be utilized advantageously even for the manufacture of shorter helical springs, since the shorter spring lengths may be severed from each other in a working step subsequent to the manufacture of a continuous, elongated spring coil. In this manner non-productive standstill periods of the winding machine may be obviated.
The apparatus of the invention may also be used to advantage in the manufacture of helical springs with a preload. The severance of shorter springs from a continuous spring coil has, in this case, the additional advantage that the wound-in preload is available to the very ends of the cut-off spring lengths.